The invention relates to a vibrometer and a method for optically measuring an object.
It is known to measure oscillations at an object in a touchless fashion using a laser-Doppler vibrometer. A typical vibrometer of this type comprises a radiation source, a beam splitter, an optic interference device, and a detector.
A source beam created by a radiation source is split via the beam splitter into a measuring and a reference beam. Using the optic interference device, which may comprise several optic components, the measuring beam is guided to the object and the measuring beam, at least partially reflected by the object to be measured is once more interfered via the interference device, together with the reference beam, to the detector, so that via the detector an interference signal can be measured between the measuring and the reference beam.
The frequency of the measuring beam is influenced by the movement or oscillation of the surface of the object such that conclusions can be drawn from the interference signal of the measuring beam and the reference beam to the movement of the object, particularly the speed of motion or the oscillation frequency of the surface of the object.
Here, the radiation source must create monochromatic radiation or at least radiation with a sufficiently large coherence length. Typically, lasers are used as the radiation source.
Furthermore, it is known to embody a vibrometer as a heterodyne vibrometer. Here, using a frequency shift unit, a frequency difference is created between the measuring beam and the reference beam. Thus, in the measuring signal of the detector a measuring signal results from the interference of the measuring beam and the reference beam with a carrier frequency, which is equivalent to the frequency difference between the measuring beam and the reference beam.
Using the heterodyne vibrometer, not only the speed of motion can be determined but also the direction of motion of the object to be measured. Furthermore, by the use of the heterodyne vibrometer, advantages can be isolated during the processing of the measuring signal, particularly technical noise in the low-frequency range.
Based on the present technical developments, particularly in micro-system technology, the measuring of increasingly smaller objects with increasing oscillation frequencies and/or speeds of motions is desirable.